The Structural Construction And Synthesis Of Organosulfur Compounds And Their Applications For Lithium-Sulfur Batteries

Lithium-sulfur batteries are considered to be a new generation of energy storage technology for the future society due to their well-known advantages,but their commercial applications are hindered by the shuttle effect of polysulfides.In the molecular structure of the organosulfur compounds,the sulfur element is covalently linked to the organic matrix in the form of C-S bond,which can effectively inhibit the shuttle effect.Especially,when the sulfur segment in the molecular structure is the short-chain formation,the electrochemical reaction of sulfur element changes to solid-solid conversion process.However,the bulk structure,low electrical conductivity and large interface resistance of organosulfur compounds cause sluggish dynamics of solid-phase reaction,so that the kinetics of organosulfur compounds needs to be further improved.As reported,organosulfur chains can reversibly react with polysulfides so that they can mediate the conversion process of polysulfides.However,most organosulfur compounds also have shuttle effect,causing the instability electrochemical performance.Hence,the microstructure and molecular structure of organosulfur compounds need to be designed and synthesized to further boost the electrochemical performance.Based on the above background,the concrete researches are as follows:1.Design and construction of organosulfur compound microspheres bonded with short-chain sulfurs(Sx,x?3):The short-chain sulfur structure can avoid the shuttle effect from the source;therefore,the mesoporous hollow aminophenol-formaldehyde resin spheres with three-dimensional network strcuture are synthesized using a self-template polymerization reaction,and then the organosulfur compounds with covalently linked short-chain sulfurs(Sx,x?3)are prepared by the steric hindrance of the three-dimensional network of aminophenol-formaldehyde resin and the inverse sulfurization method.The three-dimensional network of aminophenol-formaldehyde resin,the mesoporous hollow structure,and the sulfurization temperature benefit the formation of the short-chain sulfurs.The organosulfur compounds exhibit a solid-solid conversion process due to the covalently linked short-chain sulfurs,which effectively avoid the shuttle effect,so that the organosulfur compounds perform stably in both ether and ester electrolytes.The as-prepared organosulfur compound cathode exhibits an outstanding stable cyclability with a loss as low as 0.022%per cycle within 1000 cycles at 2.0 C.2.Design and construction of yolk-shell structured organosulfur compound nanotubes with abundant internal joints:Although the short-chain sulfurs structure brings about the solid-solid conversion reaction process,the electrochemical kinetics of the solid-phase conversion is relatively sluggish.Therefore,the yolk-shell structured organosulfur compound nanotubes with abundant internal joints are synthesized by the self-sacrificial template method and inverse sulfurization method,for boosting the electrochemical kinetics of the short-chain sulfurs structure.The yolk-shell structure with abundant internal joints of organosulfur compound could facilitate the transmission of electrons and ions,reduce the interface resistances,and fully expose the active sites of short-chain sulfurs,leading to significantly decrease the polarization and overpotential,so that it effectively enhances electrochemical kinetics of solid-solid conversion process.The organosulfur compound cathode exhibits exceptional rate performances,which displays an 841 mA h g-1 capacity at 5.0 C and a capacity reduction of 0.06%within 500 cycles at 5.0 C.The electrochemical mechanisms of solid-solid conversion process are proved on the basis of the in situ Raman spectra,in situ XRD patterns,and ex situ XPS spectra.3.Design and construction of an organosulfur compound modified separator with bifunctional redox mediation behavior:Organosulfur segments can reversibly react with polysulfides to mediate the conversion process of polysulfides.However,most reports are based on small-molecule organosulfur compounds,which can dissolve in electrolytes,causing the instability electrochemical performance.As reported in the second chapter,the C-S bond in short-chain sulfurs can reversibly react with Li2S2 and Li2S.Therefore,the mesoporous yolk-shell structured organosulfur compounds are used to mediate the redox behavior of polysulfides and stabilize the lithium metal interface.The mesoporous yolk-shell structure could facilitate the diffusion of electrons and lithium ions,and also physically block the diffusion of polysulfides.N and O heteroatoms in the molecular structure of organosulfur compound can not only play the role of chemisorption of polysulfides,but also interact with lithium ions to promote the uniform distribution of lithium ions,thereby stabilizing lithium metal.The short-chain sulfurs structure could reversibly react with polysulfides so that effectively mediating the redox behavior of polysulfides,and at the same time,it could also interact with lithium ions to inhibit lithium dendrites.Owing to the bifunctional mediation behavior of the organosulfur compound material,when it is used as a coating of PP separator,the lithium-sulfur batteries exhibit superior performance.The lithium-sulfur batteries achieve a specific capacity of 790 mA h g-1 at 4.0 C and an excellent cyclability with a capacity retention of 87%within 1000 cycles at 2.0 C.